A typical surgical tourniquet system of the prior art includes a tourniquet cuff for encircling a patient's limb at a desired location and a tourniquet instrument that includes flexible instrument tubing for connecting to the tourniquet cuff. The tourniquet cuff typically includes an inflatable portion, and the inflatable portion of the cuff is typically connected through a cuff port having a port connector to the instrument, thereby establishing a pneumatic passageway from the tourniquet instrument through the instrument tubing and the cuff port into the inflatable portion of the cuff.
Many types of surgical tourniquet systems, including tourniquet cuffs and tourniquet instruments, have been described in the prior art, such as those described by McEwen in U.S. Pat. No. 4,469,099, No. 4,479,494, No. 5,439,477 and by McEwen and Jameson in U.S. Pat. No. 5,556,415 and No. 5,855,589. Some prior-art tourniquet instruments include a pressure transducer to sense the pressure of gas at the instrument end of the pneumatic passageway and to enable the sensed pressure to be displayed for surgical staff. Many prior-art tourniquet instruments include a pressure regulator to increase and decrease the pressure of gas in the pneumatic passageway, and to maintain the pressure in the inflatable portion of the cuff near a reference pressure that is above a minimum pressure required to stop arterial blood flow past the cuff during a time period suitably long for the performance of a surgical procedure. Some tourniquet instruments of the prior art, as described for example by McEwen in U.S. Pat. No. 4,469,099, include audio-visual alarms to promptly alert users to any significant over-pressurization or under-pressurization of a connected tourniquet cuff away from a selected tourniquet reference pressure, and include audio-visual alarms to alert users to any excessive periods of pressurization of a connected cuff, because the surgical literature clearly shows that such conditions are hazardous and are associated with increased probabilities of tourniquet-related injuries to patients. A few tourniquet systems of the prior art, such as those described by McEwen in U.S. Pat. No. 4,479,494 and No. 5,439,477, include physiologic transducers to help automatically determine the minimum and safest tourniquet reference pressure required to stop arterial blood flow in the limbs of individual patients undergoing specific surgical procedures.
Tourniquet cuffs of the prior art can be grouped into three broad categories by their intended usage: (1) reusable tourniquet cuffs manufactured for usage outside the sterile surgical field in multiple surgical procedures, and for cleaning by users between successive procedures; (2) reusable tourniquet cuffs manufactured for usage within the sterile surgical field in multiple surgical procedures, and for cleaning and sterilization by specified sterilization processes between successive procedures; and (3) disposable tourniquet cuffs manufactured as sterile products suitable for usage within the sterile surgical field in one surgical procedure, and for disposal after the procedure.
Within each of these three broad usage categories, tourniquet cuffs of the prior art are supplied in a wide variety of sizes, shapes and designs matched to the intended surgical applications. Some of the largest tourniquet cuffs of the prior art are intended for use on patients having large, obese thighs with thigh circumferences of over 60 inches; such very large pneumatic cuffs typically require high tourniquet inflation pressures to stop arterial blood flow. In contrast, some of the smallest sizes of tourniquet cuffs are intended for the limbs of newborn infants, and typically require substantially lower tourniquet pressures to stop blood flow. This is an important consideration, because unnecessarily high tourniquet pressures have been shown to be associated with unnecessarily higher probabilities of injury to the patient. Some tourniquet cuffs of the prior art are designed to fit very snugly onto limbs having substantially cylindrical limb shapes at desired locations, while other cuffs are designed to fit limbs at locations that are substantially conical in shape. A close match between the limb shape and the shape of the tourniquet cuff has been shown in the surgical literature to substantially decrease the tourniquet pressure required to stop blood flow in a limb past an encircling cuff, and lower tourniquet pressures have been shown to be less hazardous for the patient.
Some designs of tourniquet cuffs of the prior art include two separate inflatable portions, often called dual bladders, for separately encircling a limb at proximal and distal locations to facilitate an anesthetic technique called Bier block anesthesia or intravenous regional anesthesia. A representative dual-bladder tourniquet cuff for Bier block anesthesia is described by McEwen in U.S. Pat. No. 5,312,431 and a representative prior-art tourniquet instrument for facilitating Bier block anesthesia is described by McEwen et al in U.S. Pat. No. 5,556,415. For Bier block anesthesia, a dual-bladder tourniquet cuff is used to perform two functions: to stop the flow of arterial blood into the limb, and to stop the outflow of an anesthetic liquid from the limb. For optimal safety in maintaining a bloodless surgical field and at the same time maintaining anesthesia in the limb, it is important that the selected cuff has a safe and appropriate size, shape and design, that the proximal and distal bladders encircling the limb are correctly identified, that the two sets of tubing from the tourniquet instrument are correctly connected to the matching proximal and distal bladders, and that the tourniquet pressure setting is appropriate for the identity and characteristics of the connected dual-bladder cuff. Any malfunction or failure of a dual-bladder tourniquet cuff during usage in Bier block anesthesia may be particularly hazardous because it may result in the sudden flow of a large bolus of anesthetic agent out of the limb and into systemic circulation, causing a possible loss of anesthesia and other anesthesia-related complications, as well as allowing a flow of arterial blood into the limb and surgical site, leading to possible blood loss and surgical complications.
Reusable tourniquet cuffs manufactured for usage outside the sterile surgical field in multiple surgical procedures, and for cleaning and disinfection by users between successive procedures, represent a common usage category of prior-art cuffs. All reusable cuffs will fail eventually, and cuff failure during surgery is hazardous for the patient. Some cuff failures may result in undetected blockages of the pneumatic passageway in the cuff, and may result in significant differences between the tourniquet pressure indicated by the instrument and the pressure actually applied by the cuff to the limb. Other cuff failures during surgery may be associated with a complete loss of cuff pressure onto the limb and may result in complications such as substantial blood loss, a sudden flow of arterial blood into the surgical site that may extend surgical time, complicate the surgical procedure and impair the quality of the surgical outcome. Also as noted above, failure of a cuff during Bier block anesthesia may additionally lead to the loss of anesthetic effect and anesthesia-related complications.
Reusable cuffs are subjected to a combination of usage conditions that will eventually result in cuff malfunction and failure, including: repeated cuff pressurization cycles, increasing cumulative periods of cuff inflation, high maximum inflation pressures, exposure to elevated temperatures, exposure to harmful cleaning or disinfection agents, natural ageing of cuff materials, and inadequate cuff maintenance and testing of functionality, materials, fasteners and connectors between uses. Any of those usage conditions may lead to cuff deterioration and failure, and the probability of such deterioration and failure increases with usage and time. In some hospitals and surgical centers, reusable tourniquet cuffs are cleaned, disinfected, visually examined and functionally tested by operating-room staff between successive usages, and tested and maintained more completely by biomedical engineering staff on a periodic basis, in accordance with established and written policies and procedures. However, this is not the case in many surgical settings. In those settings, reusable tourniquet cuffs may be cleaned or disinfected only occasionally, with various agents that may harm the cuff materials or functionality. Also in such settings, the quality of any visual examinations or functional tests of reusable tourniquet cuffs that may be performed from time to time is highly dependent on the knowledge, skill, training and vigilance of the individuals doing the tests and the time available for testing. Standardized criteria for determining whether a reusable tourniquet cuff is safe for continued usage have not yet been developed. As a result, in many settings a reusable tourniquet cuff of the prior art will continue in usage until substantial physical deterioration is obvious to experienced surgical staff and leads to its replacement, or until there is a suspected malfunction or complete failure of the reusable cuff during pre-surgical testing or during the surgical procedure itself.
Some reusable tourniquet cuffs of the prior art specifically allow sterilization by autoclaving, for use in sterile surgical fields. For example, the manufacturer of VBM reusable silicone tourniquet cuffs (VBM Medizintechnik GmbH, Robert-Bosch-Str. 7, D72172 Sulz a.N., Germany) provides autoclaving instructions and warnings. A typical process of autoclaving, or steam sterilization of a tourniquet cuff may involve the exposure of the cuff in a pressure vessel to saturated steam at an elevated temperature and pressure for several minutes to kill micro-organisms on the cuff. Although effective for sterilization, the elevated temperature, humidity and pressure of autoclaving can lead to degradation of cuff materials together with any residual cleaning and disinfecting agents on the materials, including softening, hydrolysis and changes in the physical and mechanical properties of the materials. As a result, some reusable and re-sterilizable cuffs known in the prior art have been formed of heat-resistant materials such as silicone and latex rubber. Some prior-art cuffs are accompanied by warnings that cuffs must be protected to reduce the likelihood of effects from high temperatures, humidity and pressure during autoclaving. For example, a change of cuff shape or a weakening of the retention strength of a cuff connector or a fastener from exposure of a cuff to a high temperature that persists after autoclaving could be hazardous in subsequent use. Some prior-art cuffs are supplied with a warning that the inflatable portions of the cuffs must be completely evacuated prior to autoclaving. Any rupture or weakening of the inflatable portions due to gas in the cuff during autoclaving could be hazardous in subsequent patient use. In general, suppliers of autoclavable cuffs of the prior art warn users that repeated autoclaving accelerates the natural ageing process of the cuff materials. All of the effects specified in such warnings for autoclavable cuffs serve to limit aspects of their safe usage, such as the number of inflation cycles, the cumulative inflation time, and the maximum inflation pressure before cuff failure. Any cuff failure during surgery may be hazardous for the patient, but no reusable autoclavable cuff known in the prior art includes means for limiting usage to improve safety.
Other tourniquet cuffs known in the prior art are supplied as sterile products and are intended for disposal after usage that is limited to one surgical procedure. As a result, the design characteristics of these disposable cuffs are intended to allow them to be applied and used safely and reliably within a sterile surgical field during one surgical procedure, and to be discarded cost-effectively after that procedure. For example, some disposable tourniquet cuffs of the prior art have a port that includes a very flexible thermoplastic tubing portion having a length sufficient to allow a user to easily bend the port away from the surgical site beyond the sterile surgical field for connection through a port connector to a tourniquet instrument. The various materials and components from which such prior-art disposable tourniquet cuffs are assembled are chosen to be sufficiently inexpensive to allow the cuff to be economically discarded after usage limited to a single surgical procedure, and also to be capable of sterilization by exposure to a specific sterilizing agent within a specific sterilizing process determined by the manufacturer, with no significant deterioration or change of properties that would impair the safety or performance of the cuffs after such sterilization.
Efforts have been made to reprocess and reuse tourniquet cuffs of the prior art that were originally supplied by their manufacturers as sterile products limited to a single use. Reprocessing efforts typically involve saving rather than discarding a disposable tourniquet cuff after surgery, visually examining the cuff to identify any obvious deterioration that might suggest reprocessing is not appropriate, attempting to remove any blood and other surgical debris by washing the cuffs with water combined with any of a variety of detergents or other cleaning liquids, disinfecting in some instances with various disinfecting agents, and in some cases conducting some functional tests of the cuff. Some of these prior-art disposable cuffs may be reused as non-sterile cuffs after only cleaning, or after only cleaning and disinfection, with no functional testing and with no attempt to re-sterilize the cuff. In other situations, cleaned cuffs may be re-packaged and then re-sterilized by exposure to a sterilization agent within a sterilization process that may be different from that determined by the original manufacturer to be safe and effective. Reprocessing of disposable tourniquet cuffs, with or without re-sterilization, may be carried out within hospitals or surgery centers or by third-party reprocessors, and the quality and methods of reprocessing are highly variable. Reprocessing of disposable tourniquet cuffs may result in hazards for the surgical patients on whom such cuffs are subsequently used. One such hazard arises from deterioration of cuff materials due to the use of any of a variety of chemical or physical agents that are attendant with the reprocessing, cleaning, disinfection and possible re-sterilizing processes. For example, exposure of a cuff to liquids during cleaning and disinfection may allow the liquids to enter and partially or completely block the pneumatic passageway within the port and inflatable portion of the cuff. If the cuff is re-sterilized as part of the reprocessing, any water remaining within the pneumatic passageway after cleaning may subsequently react chemically with ethylene oxide, a sterilizing agent commonly used in reprocessing, to form ethylene glycol, a sticky substance that may completely or partially block the pneumatic passageway. Repeated exposure of prior-art cuffs containing flexible thermoplastic materials to an elevated temperature during drying after cleaning or disinfection with liquids, or during re-sterilization, may soften thermoplastic materials and components, increasing the likelihood of hazardous deformation of some components, including: substantial deformation of the thermoplastic stiffener included in some prior-art cuffs that may impair the application of pressure by such a cuff to an underlying limb upon subsequent use in surgery; partial or complete blockages of the pneumatic passageways within ports or thermoplastic connectors of some prior-art cuffs; and weakening of the retention force of typical thermoplastic barb-type port connectors so that such connectors cannot establish or reliably maintain a gas-tight passageway between the tourniquet cuff and tourniquet instrument upon reuse. In general, repeated reuse of a disposable tourniquet cuff beyond the limit of usage specified by the manufacturer, including exposure to cleaning and disinfection agents and processes not anticipated by the manufacturer if reused as non-sterile cuffs, and including exposure to re-sterilization agents and processes if reused as sterile cuffs, may progressively increase the hazards for the surgical patients on whom the cuff is used.
In U.S. Pat. No. 6,682,547 McEwen et al. describe a tourniquet cuff having identification means indicative of a physical characteristic of the cuff and detectable by a connected tourniquet instrument. In U.S. Pat. App. Pub. US 20030167070 A1, McEwen et al. describe an adaptive tourniquet cuff system in which a tourniquet cuff carries identification means indicative of a physical characteristic of the cuff and in which a connected tourniquet instrument may automatically detect the physical characteristic of the cuff and adapt its operation in response to the detected physical characteristic. McEwen US 20030167070 A1 also describes the identification by a tourniquet instrument of prior exposure of a connected cuff to a potentially hazardous re-sterilization process. In pending U.S. patent application Ser. No. 11/153,667 McEwen et al. describe a disposable tourniquet cuff having means visually detectable by a user and automatically detectable by a connected tourniquet instrument to indicate exposure of the cuff to re-sterilization processes, indicating re-sterilization and possible reuse of a cuff originally manufactured and supplied as a sterile, single-use product. However, McEwen '547, McEwen US 20030167070 A1 and McEwen Ser. No. 11/153,667 do not describe means for limiting the usage of a specific tourniquet cuff so that its usage does not exceed a safe usage limit for that cuff, to improve safety. For example, the prior art does not describe apparatus for limiting the number of usages of a specific non-sterile, reusable tourniquet cuff so that usage of the cuff does not exceed a safe maximum number. Also, the prior art does not describe tourniquet apparatus for limiting the usage of reusable tourniquet cuffs manufactured as re-sterilizable cuffs to usage and re-sterilization within safe limits, including for example a limit of the cumulative inflation time, a limit of the maximum inflation pressure, a limit of the number of cycles of usage and re-sterilization, or a limit of the overall duration of usage from time of manufacture due to ageing of cuff materials. Further, the prior art does not describe apparatus for limiting the usage of a single-use tourniquet cuff to usage within safe usage limits, and to usage in only one surgical procedure, without relying on the detection of re-sterilization to indicate possible reuse, because some users may attempt to reuse single-use cuffs as non-sterile cuffs, without exposing them to re-sterilizing agents and re-sterilization processes between successive usages. There is a need for tourniquet cuff apparatus for limiting usage as described above to improve safety, and the present invention addresses that need.